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Concrete Calculator

Calculate concrete volume and number of premix bags needed for slabs, posts and footings.

Slabs & PostsAU Measurements

About

Calculate concrete volume and number of premix bags needed for slabs, posts and footings.

How It Works

Ordering too little concrete means stopping halfway through a pour to wait for another delivery — which is a real problem once the first batch starts setting. Ordering too much means paying for material you don't use and finding somewhere to dispose of it. Getting the volume right before you order matters.

This calculator works out the cubic metres of concrete needed for slabs, footings, columns, and steps. Enter your dimensions and it gives you the volume plus a suggested order quantity with a small waste margin — typically 5-10% — to account for spillage and minor variations in ground level.

Concrete is ordered and priced by the cubic metre. One cubic metre weighs roughly 2.4 tonnes. For anything beyond a small garden project, ready-mix delivery from a concrete plant is almost always easier and not necessarily more expensive once you factor in your own time and the physical effort of hand-mixing.

How to use it

  1. Select your shape — slab, footing, column, or steps.
  2. Enter the relevant dimensions in metres.
  3. Click Calculate to see the required volume in cubic metres, with a recommended order quantity including a waste margin.

Frequently Asked Questions

Ready-mix concrete prices vary by location and mix specification, but as a rough guide expect $250–$350 per cubic metre delivered. Small-load surcharges apply for orders under about 3m³ — if your job is small, bagged concrete mix from a hardware store may be more practical despite the higher per-m³ cost.

For standard paths and garden slabs, 20MPa is typical. For residential floor slabs and patios, 25MPa. For driveways that take vehicle loads, 32MPa is more common. If an engineer has specified a particular strength, use that — don't substitute a lower grade to save money.

Garden paths: 75–100mm. Residential patios and floor slabs: 100mm. Driveways for passenger vehicles: 100–125mm. Driveways for heavy vehicles or trucks: 150mm minimum. Always check against your local council requirements and any engineer's specification for your project.

Concrete reaches about 70% of its design strength at 7 days and full strength at 28 days. You can walk on it after 24–48 hours and drive on it after 7 days, though heavier loads should wait the full 28-day cure period. Keep it moist during curing in hot or dry weather — this is one of the most commonly skipped steps and it matters.

Ground surfaces are never perfectly level, formwork isn't always exactly the right dimensions, and some spillage is inevitable during a pour. A 5–10% buffer ensures you don't run short. Running out of concrete during a pour is a much bigger problem than having a small amount left over.

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